1. Field of the Invention
The present invention relates to a semiconductor device and in particular to a semiconductor device that is provided with an insulated gate bipolar transistor (IGBT), a metal oxide semiconductor field effect transistor (MOSFET), and a control integrated circuit (IC).
2. Description of the Related Art
Inverter circuits in power supply devices and motor control devices generally use power semiconductor elements of IGBTs or MOSFETs. IGBTs exhibit small ON resistance in a range of high withstand voltage and high current while MOSFETs exhibit small ON resistance in a range of medium and low withstand voltage and low current. Patent Document 1 and Patent Document 2 disclose semiconductor devices exhibiting a characteristic of small ON resistance in the whole range of from low withstand voltage to high withstand voltage and from low current to high current by utilizing those characteristics of IGBTs and MOSFETs.
A semiconductor device composes an intelligent power module (IPM) comprising a power semiconductor element and a control IC that includes a driving circuit for driving the power semiconductor element and a protection circuit, all components being incorporated in a single package.
FIG. 7 is a circuit diagram showing an example of a conventional semiconductor device provided with an IGBT and a MOSFET.
This semiconductor device is composed of a power semiconductor element 100 and a control IC 101. The power semiconductor element 100 comprises an IGBT 102 and a MOSFET 103 connected in parallel. The emitter of the IGBT 102 and the source of the MOSFET 103 are connected to a terminal E and a terminal S0 of the power semiconductor element 100. The collector of the IGBT 102 and the drain of the MOSFET 103 are connected to a terminal C of the power semiconductor element 100. The gate of the IGBT 102 is connected through a resistor 104, to a terminal G0 of the power semiconductor element 100. The gate of the MOSFET 103 is connected directly to the terminal G0 of the power semiconductor element 100. The diode 105 that is anti-parallel-connected to the MOSFET 103 is a body diode formed at the MOSFET 103 and functions as a free-wheeling diode for circulating the current flowing from the terminal E of the power semiconductor element 100. The terminal S0 and the terminal G0 are connected to a terminal U0 and a terminal T0 of the control IC 101, respectively.
The power semiconductor element 100 having the IGBT 102 and the MOSFET 103 connected in parallel exhibits a low ON resistance in a low current range thanks to a characteristic of the MOSFET 103, which reduces steady-state loss. While in a high current range, the characteristic of the IGBT 102 works to avoid breakdown of the power semiconductor element.
A resistor 104 having a high resistance value is connected to the gate of the IGBT 102 to allow the MOSFET 103 to turn ON first and then the IGBT 102 to turn ON when the power semiconductor element 100 turns ON. This decreases a feedback capacitance and reduces a turn ON loss.
The control IC 101 is provided with an overcurrent protection circuit though not indicated in FIG. 7. The overcurrent protection circuit monitors the current flowing through the emitter of the IGBT 102 at the terminal U0. When the current through the emitter exceeds a predetermined threshold value, the potential at the terminal T0 is forced to drop, turning OFF the IGBT 102 and the MOSFET 103.
A half-bridge inverter circuit can be constructed by making up a totem-pole circuit with a semiconductor device having the structure described above and another semiconductor device having the same structure and by connecting the power semiconductor elements of the two semiconductor devices in series. Such an inverter circuit can convert a DC voltage to an AC voltage by ON-OFF-controlling the power semiconductor elements in the high side arm and the power semiconductor elements in the low side arm.
[Patent Document 1]
Japanese Unexamined Patent Application Publication No. H04-354156 (FIG. 2 and FIG. 5, in particular)
[Patent Document 2]
Japanese Unexamined Patent Application Publication No. 2014-130909 (FIG. 5, in particular)
If a short-circuit accident occurs in the semiconductor device in the high side arm during an ON controlled period of the power semiconductor element in the semiconductor device used in the low side arm, the control IC detects overcurrent of the power semiconductor element and turns the power semiconductor element OFF. The abrupt drop of the collector current of the power semiconductor element results in a fast rise in the collector voltage, which may reach the withstand voltages of the IGBT and the MOSFET. The IGBT and the MOSFET are turned OFF nearly at the same time upon detecting the overcurrent. Thus, the power semiconductor element carries a heavy current under the condition of high voltage application. Consequently, a short-circuit guarantee time, which is a time period until a semiconductor element is broken down, is determined by the property of the IGBT which exhibits a shorter short-circuit guarantee time. Thus, the semiconductor device exhibits a low short-circuit tolerance.